Alex Salmond and Nicola Sturgeon, pictured in 2014, met twice at her Glasgow home, once in Aberdeen, and spoke twice on the phone about the former first minister’s sexual harassment allegations.
Photograph: Murdo Macleod/Guardian

Opposition parties have challenged Nicola Sturgeon, Scotland’s first minister, to justify her decision to have a series of discussions with Alex Salmond about sexual harassment allegations against him.

Scottish Labour and the Scottish Tories said those private discussions, two of which took place in Sturgeon’s home, raised further serious questions about the Scottish government’s botched investigation into two harassment complaints against Salmond.

Sturgeon’s government admitted in court on Tuesday that a key civil servant’s conflicts of interest in the case rendered its investigation unlawful and potentially biased.

Salmond, Sturgeon’s predecessor as Scottish National party leader and first minister, insisted that Leslie Evans, Scotland’s chief civil servant, should resign for overseeing the inquiry. But Evans was defended on Wednesday by Dave Penman, the general secretary of the First Division Association, the union which represents senior civil servants.

Penman accused Salmond of pursuing a personal vendetta against Evans. He said the FDA believed the Scottish government should reinvestigate the harassment claims once a separate Police Scotland criminal inquiry into the alleged assaults was completed.

The Tories intensified the pressure on Wednesday by calling for the Scottish parliament to launch its own inquiry into the affair. A Labour source suggested the party backed those calls. “We need to get to the bottom of how that happened – and that includes Nicola Sturgeon’s multiple meetings and conversations with Alex Salmond,” he said.

“It’s not credible or sustainable for the first minister to claim these were not government meetings, it was reckless for her to meet with him on multiple occasions and people deserve to know why she exhibited such poor judgment and what was said.”

Salmond disclosed he had met Sturgeon three times to lobby her when news of the investigation leaked to the Daily Record in August last year. He said he had told her about his attempts to offer mediation or arbitration to get the two sex harassment cases settled.

Sturgeon confirmed then that several meetings had taken place but on Tuesday acknowledged for the first time she had met her former mentor and close friend three times and had two further telephone calls over a 15-week period.

Two meetings took place at her Glasgow home, on 2 April and 14 July, and a third time on 7 June before an SNP conference in Aberdeen. She had two telephone calls with him, on 23 April and 18 July, but they had not met or spoken since, she said.

She told MSPs on Tuesday she had “firmly” told Salmond she had no role in the process and denied the meetings were improper, since they were not government meetings.

“I did not intervene or seek to intervene. Self-evidently I did not, because what Alex Salmond was seeking did not happen. That is the important principle – and one on which I am absolutely satisfied,” Sturgeon said.

Pauline McNeill, Scottish Labour’s equalities spokeswoman, said that was not credible. Sturgeon had to explain why no civil servant was present, why they were not listed in her official ministerial appointments record, and whether she had notified Evans that the meetings had taken place or written up a note about the contacts.

“These were discussions between the current first minister speaking with a former first minister about a Scottish government investigation into alleged misconduct in office,” McNeill said. “Your decision to meet and hold phone calls with Mr Salmond on multiple occasions about the investigation could have compromised the investigation.”

Opposition suspicions have been fuelled by the disclosure that Sturgeon’s private secretary, John Somers, and her chief of staff, Liz Lloyd, were due to appear in court on Monday to be questioned by Salmond’s lawyers about the case.

That appearance was cancelled after the Scottish government decided late last week to accept defeat. Salmond’s legal team believes more evidence about the government’s mishandling of the case may have emerged but a Scottish government spokesman said it was “ridiculous and utterly unfounded” to suggest the two were linked.